PARR, WILLIAM, Marquis of Northampton (1513–1571), was only son of Sir Thomas Parr, K.G. (d. 1518), of Kendal and of Greens Norton, Northamptonshire, by Maud (d. 1531), daughter and coheiress of Sir Thomas Green of Greens Norton and Boughton; he was nephew of Sir William (afterwards Lord) Parr of Horton (d. 1546) [see under Parr, Sir William, 1434–1483?], and brother of Catherine Parr [q. v.] Born, probably at Kendal Castle, on 14 Aug. 1513, he was educated at Cambridge under Cuthbert Tunstal [q. v.], who was one of his father's friends. His father died on 12 Nov. 1518, and he succeeded to the estate. He was knighted on 18 Oct. 1537, took part against the northern rebels, was one of those who tried the Lincolnshire prisoners in 1538, and was created Baron Parr and Ros of Kendal on 9 March 1539. On 16 Dec. of the same year he was made keeper of the parks at Brigstock. On 25 May 1540 he became steward of the manor of Writtle, Essex, and in November following captain of the band of gentlemen-pensioners. In 1541 he was keeper of the park at Moulton, and had trouble with the tenants there. When it was decided that his sister Catherine should marry Henry VIII, he naturally received additional preferment. In March 1543 he became a privy councillor, and lord warden and keeper of the marches towards Holland; he was also placed upon the council of the north, and made K.G. on 23 April 1543. On 23 Dec. 1543 he was created Earl of Essex, this title being chosen because it had, in 1539, become extinct on the death of his father-in-law, Henry Bourchier, second earl of Essex [q. v.] Cromwell had been created Earl of Essex in April 1540, but was executed three months later. Parr also received in 1543 the barony of Hart in Northamptonshire. In the expedition to Boulogne in 1544 Essex was chief captain of the men-at-arms; and, as a further proof of Henry VIII's confidence in him, he was an assistant-councillor to the king's executors, Henry leaving him 200l. by his will. He was one of the commissioners for the trial of the Earl of Surrey on 13 Jan. 1546–7.

Essex was one of the commissioners to determine claims at the coronation of Edward VI on 5 Feb. 1546–7, and on the 15th of the same month was created Marquis of Northampton. He was a prominent supporter of Somerset, and was called to the privy council on 12 March 1546–7. On 24 June 1549 he was at Cambridge, and heard the disputations as to the sacrament of the altar. In July 1549 he was created lord-lieutenant of Cambridgeshire, Bedfordshire, Huntingdonshire, Northamptonshire, and Norfolk, and went against Kett in the same month to raise the siege of Norwich. He was evidently no general, and Kett easily defeated some of his troops. He was therefore deprived in August of the command, which was given to Dudley. On 4 Feb. 1549–50 he was created great chamberlain; in April he was one of those who received the French hostages after the surrender of Boulogne. In June 1551 he conducted an embassy to France to invest Henry II with the order of the Garter; and he was one of those commissioned to suggest the marriage between Edward VI and the French king's daughter. In the autumn of 1551 Margaret of Scotland paid a visit to the English king, and Northampton, who was still in command of the band of gentlemen-pensioners, received her at Hampton Court. In the same capacity he was fourth captain in the great muster held before the king in Hyde Park on 7 Dec. 1551.

Northampton was a friend of Northumberland, hence his influence had grown on Somerset's fall; Somerset's conspiracy was supposed to be directed against Northumberland, Pembroke, and Northampton. He duly signed the instrument of the council agreeing to the succession of Lady Jane Grey, and went with Northumberland into the eastern counties to maintain her cause. After Queen Mary's triumph he was committed to the Tower on 26 July 1553, and on 18 Aug. was arraigned and condemned to be executed. He was attainted and deprived of the Garter, but he was released from the Tower on 31 Dec. 1553, and pardoned on 13 Jan. 1553–4. Arrested again on suspicion of complicity in Wyat's insurrection on 26 Jan., he was released once more on 24 March 1554. He was also restored in blood on 5 May 1554, but he was not restored to his rank, and was known during the rest of Queen Mary's reign as Sir William Parr; he only recovered part of his estates. Doubtless his relationship to the queen-dowager accounted for the mercy shown him.

On the accession of Queen Elizabeth his fortunes revived. He was made a privy councillor on 25 Dec. 1558, and was one of those whom the queen consulted respecting the prayer-book. He became once more Marquis of Northampton on 13 Jan. 1558–9. When the trial of Wentworth for the loss of Calais took place on 20 April 1559, Northampton acted as high steward. He was again made a knight of the Garter on 24 April 1559; on 22 July 1559 he was one of the commissioners to visit the dioceses of Oxford, Lincoln, Peterborough, and Coventry and Lichfield, and in October of the same year received the Prince of Sweden, then on a visit to England. He is mentioned as a member of Gray's Inn in 1562. On 18 March 1570–1 he was created M.A. by the university of Cambridge. Elizabeth seems to have liked him. She stopped to inquire about his health, when he was ill with an ague, on her way into London both in November 1558 and on 6 July 1561. When he died, on 28 Oct. 1571, at Warwick, she paid for his funeral at St. Mary's Church there. In spite of considerable traffic in abbey lands and of grants made to him at his sister's marriage and later, he did not die rich.

Northampton had a most unfortunate matrimonial history. He married, first, in 1541, Anne, daughter of Henry Bourchier, second earl of Essex. In 1547 he divorced her, and, apparently before the proceedings were properly completed, he married Elizabeth Brook, daughter of Lord Cobham. He had to separate from her for a time in order to get an act of parliament passed, in 1548, to make any children of his first wife illegitimate (a printed copy of this act is in the British Museum). In 1552 he procured another act to secure the legality of his second marriage. The second marchioness was influential at court, and helped to bring about the marriage of Lord Guilford Dudley and Lady Jane Grey. One of the earliest acts of parliament in Queen Mary's reign repealed the act of 1552, so that the position of the marchioness was one of some uncertainty. On her death in 1565, Northampton married, thirdly, Helena, daughter of Wolfgang Suavenberg, who was either a German or a Swede. He left no issue, and what property he had passed to his nephew Henry Herbert, second earl of Pembroke [q. v.], son of his sister Anne.